Jealousy
by mew-tsubaki
Summary: Oneshot, slash, post-spring high, light spoilers for Extra Game. "There are childhood friends. And then there are ambiguous relationships." -—Or, Iwaizumi thinks it's not such a great thing, having his cousin around. *Set after "Crossing Paths" & followed by "Future Plans."


**Jealousy**

A Haikyuu!/Kuroko no Basuke crossover

by mew-tsubaki

Note: The _Haikyuu!_ characters belong to Furudate Haruichi-sensei and the _Kuroko no Basuke_ characters to Fujimaki Tadatoshi-sensei, not to me. I can't seem to escape this AU… Read, review, and enjoy! * Note: Set after "Crossing Paths," but you don't have to read that to enjoy this. You might like to, though. :)

\- ^-^3

There are childhood friends. And then there are ambiguous relationships.

Iwaizumi Hajime knows this distinction all too well. Or, at least he thinks he does as he wakes up on a Friday morning in early June. He sits up slowly, propping himself up with his right arm and running his free hand through his messy black hair. He exhales slowly, lowly, and the weight on the bed shifts. His eyes drift to his right at the cause of the shift.

Oikawa Tooru's breathing is steady and nearly silent in the quiet of their university dorm room. He has his head on his pillow, and his hair isn't as mussed up as it can be most mornings. He jostles one more time, makes a face, and then yawns, telling Iwaizumi he's awake. "…mff," he says by way of greeting.

Iwaizumi snorts. "Good morning to you, too," he mumbles. But where, once upon a time, he would've said it with major attitude because that was always the kind of reaction Oikawa provoked in him, he now says such things in a gentler tone. Frankly, being with Oikawa for almost their whole lives…it's finally made him go soft.

(Or maybe Iwaizumi's just trying harder, after seeing how his cousin, Yukio, is around the object of his own affections.)

The dark-haired man doesn't shove Oikawa or anything as he turns and swings one leg off the bed. It'd be disastrous, doing that. There are two beds in their room—of course there are, because the university was lodging two people in there—but eventually Iwaizumi found that one bed seemed to be all they needed, because somehow university escalated things for them so quickly that it turned out to be more natural for Oikawa always to be within reach. And he knows Oikawa thinks the same. But one bed for two people is a bit of a stretch, especially with someone tall like Oikawa and someone muscled like Iwaizumi occupying the same space.

Oikawa flops onto his back and just opens his eyes as Iwaizumi kicks his friend's clothes around on the floor to get to his own clothes drawer. "Ah," the setter begins to complain. "Can't we just stay in today? Play hooky?"

Iwaizumi's affections for Oikawa are snuffed out in that second. "You're joking, right? We've got practice! If you're not going to be serious about it just because—"

"No, no, I'm serious." Oikawa sits up and stares at Iwaizumi, initially with a frown. But then the frown melts into a smirk. "Hey, Iwa-chan… Aren't you going to change out of your pajamas~?"

Iwaizumi throws a shoe at his head, turning so Oikawa doesn't see his red face. "Not with you watching, Shittykawa!"

\- ^-^3

Some days, going to practice, sadly, is the worse of two bad options.

Oikawa too easily goes from groggy flirt to maniacal overlord as soon they enter the gym and find that, due to Oikawa's laziness making them late, Ushijima is one of several people to have arrived first.

Oikawa gnashes his teeth. "Ushiwaka…!"

Iwaizumi rolls his eyes and internally groans. It's been the same thing since middle school, except now Ushijima Wakatoshi is their teammate, for the first time ever. He transferred at the start of this, their second year of university, deciding T Uni had the sports program he preferred over what was offered at K Uni. But it still doesn't seem to register with the guy that Oikawa genuinely hates him, not just finds him his rival.

"You're looking stupid today, Ushiwaka-chan!" the setter hollers at Ushijima as the taller man stretches.

Ushijima responds in kind with a look that's something like "Huh? Did you say something?"

Which only serves to annoy Oikawa even further.

Iwaizumi sighs. Ushijima is just another volleyball idiot like Kageyama, when it comes down to it.

"Iwaizumi-san, coach said we've got flying falls to practice first," Yahaba says.

Thank god for Yahaba. Watari, too. As soon as he thinks of their names, Iwaizumi smiles his thanks at Yahaba, and his eyes spy Watari towards the back of the room, pulling on his kneepads. Sure, Watari had had to try twice to get into their school whereas it was easy for Yahaba, but Iwaizumi truly is grateful that he's no longer the only person on their team who knows how to deal with Oikawa. With them around, it's easier to keep tabs on Oikawa. And _that_ makes practice ten times better.

Practice does in fact begin with flying falls, as Yahaba mentioned, and then T Uni's volleyball club works on receives. There are countless things to practice, to improve on, but it's just like any other day for the athletes. These things don't really feel like work, even if there are activities that make them feel the burn, because they've all been at it for nearly half their lives—otherwise they wouldn't have made it onto the team. Only a handful of guys began their volleyball careers late in life, in their second or last year of high school at the latest, but it shows, because those guys aren't regulars. Iwaizumi's already a regular, though, as is Oikawa. It won't be long before their coach finally stops hazing Ushijima and makes him a regular, too, and Iwaizumi hopes that the staff won't wait until next year to make Watari their regular libero. Things are falling into place perfectly for T Uni's team, really.

Hours and a good, heart-pounding practice match later, practice ends, and Iwaizumi drains his water bottle. He turns to his right to ask Oikawa if he wants to join him to refill…but the setter isn't there.

Iwaizumi blinks, but it's not as though Oikawa would leave practice without him. No, he's just sitting off to the side, checking his phone.

"Oi. Shittykawa," the spiker calls out to his childhood friend.

"Yep, Iwa-chan," Oikawa replies automatically, not even glancing away from his phone when he says it. Whatever he was doing, he finishes, and he releases a big breath as he stashes his phone back in his bag. Then he's all sparkly, big eyes. "What?"

Iwaizumi feels the onset of heartburn, seeing that sappy expression on Oikawa's face. "Nothing. Are you ready to go?"

"Ah, actually." The setter stands up and runs his hand along the back of his head, mussing with it. His eyes dart up and to the left. "Something came up that I have to take care of…"

"That's the first I've heard." Iwaizumi slings his towel over his shoulder. "Well, we have the same schedule today, so I've got nothing to do—I can join you."

Oikawa smiles, but it's not the usual kind of smile that only Iwaizumi sees…it's that infuriating one that the idol tends to dole out to his fangirls. "Ah ha…not really, Iwa-chan… I'll catch you at home, okay?"

Iwaizumi won't deny that he's annoyed, but it'd be a waste of time to make a complaint about something this minor. "Yeah, okay, okay…"

It really says something about them, that they've come this far and can handle a scenario like this without any of Oikawa's usual flamboyancy or Iwaizumi's hotheadedness. Frankly, if no one were around, Iwaizumi could even picture Oikawa trying to steal a kiss to make up for his absence.

…not that Iwaizumi would allow it. But still.

So Oikawa goes off on his own, and the rest of the club disperses. Yahaba catches up with Iwaizumi, and the two decide to grab lunch together before the younger male heads to class, and it's just another day in their college lives.

\- ^-^3

But that was yesterday, and this is today.

"Ahm…I've got plans, sorry, Iwa-chan." Oikawa winks and looks half-serious when he apologizes. But Iwaizumi's irked more than before.

"You gave me the impression that yesterday was just a one-off," the spiker informs him as they stand awkwardly by the door, Iwaizumi posed ready to go with Oikawa as is their usual routine. But now his hand is on the strap of his bag, and his grip is too tight.

"Sorry. I didn't mean to—I just—" Oikawa sighs. "Look, when I get home, I'm all yours, okay? Promise." There's a glint in his eyes that tells Iwaizumi that he means it.

The shorter man hates the shiver that plays his vertebrae like piano keys, and he looks away. "All right," he concedes, though his patience is wearing thin.

Oikawa prances off without another word, and Iwaizumi stomps angrily out of the gym, dragging his feet on the way to the dorm. He thumbs his cellphone in his pocket, and he doesn't make up his mind to call Yukio until he's back at his room, unlocking the door.

The line rings once, twice, three, four times. Iwaizumi waits and continues to let it ring, because he knows his cousin. Yukio can easily get absorbed in other things, so sometimes it takes him a while to answer his phone. But he always answers…

…except for this time.

Just like Oikawa ditching him, Yukio not answering him is another break from the norm. What's with them? They're the two most dependable people in Iwaizumi's life, and now things don't feel right at all.

It makes it that much harder for Iwaizumi to sit still after he showers and changes into clean clothes. He whips up a small snack and tries to get some studying done as the clock ticks away, noting the time that passes in Oikawa's absence.

By the time Oikawa comes home, it's late and Iwaizumi's exhausted. And Oikawa has nothing to say for himself.

"I'm home, Iwa-chan," Oikawa says softly, dropping his bag inside the door and passing by Iwaizumi to have a bit of physical contact before he showers.

Iwaizumi relishes the familiar, homey warmth of the setter's long fingers, and he holds onto them, even though Oikawa moves to head to leave for the bathroom.

Oikawa stares at him. Then his easy smile appears on his face, and he pecks the top of his ace's head. "I'm home," he repeats.

It's all Iwaizumi needs in that moment, and he could care less about where Oikawa's been, now that he's back.

Now that he's here.

\- ^-^3

Two more days, and Iwaizumi's temper builds up. Maybe he could handle not knowing the truth on Saturday, but it's Monday already, for crying out loud. What the hell is wrong with Oikawa, the guy who can't keep a single secret even if his life depended on it?

Oikawa's character does not fail Iwaizumi, though. No doubt the setter has been keeping an eye on Iwaizumi, too, and he bursts when the twosome grabs dinner at a nearby udon shop that night. "I've…been hanging out more with Yukio-chan."

Iwaizumi blinks. Huh. Not what he was expecting. Granted, it had been unexpected enough when, last fall, they'd come across Yukio in the city and had met his better half, Kise, at the same time. Naturally, his question is, "And Kise?" That'd make sense. Disturbingly, Oikawa and Kise had gotten along in the end, which had only frightened the cousins more than the two pretty boys spatting.

Oikawa sips the broth in his bowl. "No, just Yukio-chan and me."

O…kay. Again, not expected. Iwaizumi doesn't believe it to be the strangest of occurrences, but still. Why not hang out with both Yukio and Kise? The more Iwaizumi thinks about it, even as they finish supper and go home, the more he supposes it makes sense. Kise's in his last year of high school by now, so it's probably harder for him to come to Tokyo and see Yukio when he wants to.

But still, that night finds Iwaizumi lying awake, his mind unable to turn off. What gives? He, Oikawa, and Yukio had grown up together, playing together in the summer when Yukio would come to stay at Iwaizumi's in Miyagi. Iwaizumi and Yukio had always been close—Yukio was only a month younger than him!—but to hear from Oikawa that they'd been spending time together, and Yukio had yet to return his missed call? Really, what gives?

Oikawa yawns in his sleep, and Iwaizumi glances his way, though he can barely see anything in the dark.

Iwaizumi and Yukio had always been close…but Oikawa and Yukio were pretty close, too. Oikawa has never rubbed Yukio the wrong way he does Iwaizumi, and those two have always been on a first-name basis, even to the point of annoying Iwaizumi. God, even over a year ago, when they'd been on the phone, Iwaizumi could recall hating hearing Yukio refer to Oikawa as "Tooru" too easily. Something clicks into place for Iwaizumi in that moment, then, and the worst thing possible occurs to him:

Maybe Oikawa is thinking he chose the wrong childhood friend.

Another yawn from Oikawa makes Iwaizumi jolt, but the setter remains asleep. Iwaizumi watches him for a moment longer, exhales slowly, and turns on his side, away from Oikawa.

There are childhood friends. And then there are ambiguous relationships.

But Iwaizumi's beginning to think that maybe things aren't as ambiguous between them as he once thought.

\- ^-^3

One of Oikawa's political science classes is at the same time as one of Iwaizumi's breaks on Tuesday, so the spiker seizes the opportunity and texts Hanamaki and Matsukawa, asking them to hang out for a bit.

Twenty minutes later, Iwaizumi's treating them to some ice cream at a shop near Hanamaki's school, which is kind of the halfway point between Iwaizumi's and Matsukawa's schools. "Ahh, I thought you were growing tired of us, Iwaizumi," Hanamaki teases before he takes a gigantic bite of his sundae.

"Hardly. Who started that online mission at midnight last week? I don't even like that videogame," Iwaizumi reminds him with a look.

"So spill. What can the A Team do for you?" Sharp as ever, Hanamaki and Matsukawa know Iwaizumi all too well and are all ears.

So Iwaizumi complains a bit. He confesses that… _maybe_ , just maybe he's beginning to fret for real about how close Oikawa is to his cousin. Only when he finishes his tale does he realize how it sounds to his ear, and that he and Oikawa never informed them about…well, _them_. Oh, hell.

Yet Hanamaki and Matsukawa, to their credit, don't tease him, nor are they very surprised. Instead, Hanamaki passes Matsukawa some money and grumbles "Dammit" under his breath.

"What?" Iwaizumi asks.

"Oh, I thought you two were doing the do ages ago, but Matsukawa said it would start after we graduated, so I just lost a bet. Thanks, Iwaizumi," Hanamaki says bitterly, finishing his sundae.

The ace doesn't know how to respond. So many things annoy him about the situation—that their friends bet on them, that their friends were way too invested in their private matters, that their friends don't appear to have heard a word he said of the problem at hand—that Iwaizumi takes a calming breath and glosses over the bet for a moment. "Yeah, well, things happen."

"Yeah, they do," Hanamaki jokes, and he ends up with a spoon thrown at his face mysteriously from Iwaizumi's direction.

"Ah, Iwaizumi…," Matsukawa says. "Calm down. Are you really that worried about Oikawa and your cousin?"

Good old Matsukawa heard him out, of course. Iwaizumi furrows his brow. "Honestly…I don't know. I mean, I know the two of them, so I can't really picture it, but Oikawa's so damn fickle sometimes…"

"Nah, not to you—he's too damn loyal, if you ask me," Hanamaki pipes up, rubbing his chin where the spoon connected. He waves Iwaizumi off, uninterested. "You're overthinking things, which is Oikawa's job. Just tell our genius setter what's on your mind, otherwise it'll never occur in that thick head of his that he's upset you."

"'Our genius setter'?" Matsukawa pokes fun at him.

"Yeah, yeah, old habits die hard, so sue me," the tawny-haired man retorts, reaching for a spoonful of Matsukawa's ice cream, but Matsukawa downs it before Hanamaki gets any.

Iwaizumi chuckles to himself, watching the two of them and missing their time at Seijou when things were so much easier. Then again, things were different in high school and had yet to evolve into what they are today…and Iwaizumi knows he'd miss things the way they are now if he were to go back and relive their Seijou days, even for one day.

\- ^-^3

Taking Hanamaki's advice is easier said than done, however. Oikawa skips out on him a couple more times the next two days, and still Yukio hasn't called his cousin back, or even texted him. Even for Iwaizumi, there's only so much he can do to rein in his temper.

Friday arrives, marking a week's passing since Oikawa began acting strange…er, stranger than normal. Iwaizumi gets up as usual and dresses as usual.

Oikawa, on the other hand, makes no quips about wanting to watch the dark-haired man change. Instead, he, too, gets out of bed and changes.

Go figure. He probably just doesn't want to be shown up by Ushijima again.

Practice begins with some stretches and some spiking, but the coach quickly arranges teams so they can fit in two practice matches today. Oikawa begrudgingly heads to Ushijima's side of the court, and Iwaizumi is on Yahaba's side, along with Watari. Some of the senior members divvy themselves up, and the first of two matches is off to a good start. It sucks that Oikawa and Ushijima really do make a good team, but Iwaizumi manages to push a few tosses through which Oikawa catches with his face. It's almost as if divine punishment exists and has sided with Iwaizumi in the recent ridiculousness.

The first match ends by a slim win in the favor of Iwaizumi's side. The second match quickly goes to Oikawa, though, and signals the end of that day's practice.

Unfortunately, when things end this time around, Yahaba and Watari are some of the first to leave, so no matter what happens with Oikawa, Iwaizumi can't use his kouhai as an escape route this time. So he just sighs and packs up and, calmly as he can, waits for Oikawa. But truly he's expecting Oikawa to skip out on him again.

That's why it comes as such a surprise when Oikawa releases a huge sigh, dries his face on his towel, and throws Iwaizumi a smile. "Good game today, Iwa-chan."

His attitude's disarming. "Uh…yeah."

"But did you have to aim for my face in the first game?" Oikawa grouses, rubbing his right cheek before pressing his water bottle against it. "Ah, it still stings…"

Iwaizumi's not sure how to respond. Funny how it takes only a week for him to forget how to interact with this doofus. "So…," the shorter male prompts.

Oikawa blinks at him, his smile back. "What?"

"You're not leaving, to hang out with Yukio or otherwise?"

The setter laughs and pats Iwaizumi on the arm. "Oh, Iwa-chan, I'm sorry about recently, really. But nope, I'm all yours." He says it so genuinely that it's hard not to forgive the dumbass for causing Iwaizumi any worry in the first place.

So Iwaizumi curses under his breath. "Fine, whatever. But lunch is on you today, Shittykawa," he states, stomping out of the gym almost too quickly for Oikawa to catch up.

"Wah, Iwa-chan, wait~!" Oikawa falls into step with him and steers him off-campus. "All right, all right… You win! What do you want for lunch? Maji Burger, maybe?"

They haven't been there in a while, so Iwaizumi supposes it's as good a place as any. It's one train stop away, anyway, so it's not as though it's much of an inconvenience.

Outside the fast food joint, Oikawa slows and tugs on Iwaizumi's arm. "And, by the way, happy birthday, Iwa-chan."

Iwaizumi pushes the door open. "You're only saying that n—"

"HAPPY BIRTHDAY~!"

Maji Burger—of course. It's not as though they go there very often. But it's still a guaranteed surprise to see all the familiar faces gathered in one spot. All of their friends are there—Hanamaki, Matsukawa…ah, so this is where Yahaba and Watari scarpered off to…they even managed to call up Kindaichi and Kunimi!

Poppers go off in his face as he and Oikawa join them, and another familiar face appears in his line of sight: Yukio. "Happy birthday, Hajime," he says, and he's wearing a stupid grin on his face that reminds Iwaizumi of when they were little.

This surprise couldn't be any better, truly. The party is great, and everyone has a good time. Iwaizumi likes his gifts, though he would've been fine even without them.

Yukio pulls him aside when Hanamaki and Matsukawa decide to arm-wrestle over the last slice of cake, and Oikawa joins them. Both he and Yukio look like puppies with their tails between their legs. "Hajime—sorry!" his cousin explodes with a sharp bow, and he shoves Oikawa's head down, too.

Iwaizumi gives them a look. "What are you on about? I didn't see this coming—and I love it. There's nothing to be sorry for."

"No…" Yukio looks at him. "I never called you back or anything. And I'm sorry for dragging Tooru around with me," he adds while Oikawa twiddles his thumbs. "We set this whole thing up, but we went shopping together first. Ryouta's birthday is only eight days after yours, so…we were helping each other out, picking out gifts."

The explanation is unanticipated, but it definitely explains everything, and Iwaizumi finds that his temper is deflating the longer he eyes their sorry expressions. He sighs and runs a hand through his hair. "All right, all right, I forgive you. I guess that's the only story that makes sense." He twists his mouth around. "I confess…I thought you were just leaving me out of things, maybe…for some other reason."

Kasamatsu Yukio gets along with his cousin not just because they're cousins but because they think along the same lines. So he reads between the lines easily here and laughs it off. "Hajime, _really_? Me and Tooru? There's no way I'd ever like him that way."

Oikawa's the last to get it. But still—"Ouch, Yukio-chan! Really?!"

"It's because I know you," Yukio deadpans. And the howl that Oikawa emits makes the cousins laugh.

\- ^-^3

At the end of the night, Iwaizumi and Oikawa are in their dorm room, which now has even less space in it than before because of all the gifts. The giant stuffed Godzilla from Hanamaki, who's ace at crane games, might've been a bit much, but Iwaizumi can't deny it adds a certain charm to the room.

"Don't tell me that's your favorite gift," Oikawa bemoans as they settle in front of the TV and he passes Iwaizumi a cup of tea.

"Maybe," Iwaizumi suggests, placing the plushie between the two of them.

"Oh, c'mon, Iwa-chan! I said I was sorry…! Besides," he huffs, smooshing Godzilla's head down and out of the way, "didn't you like my gift?"

It's true. He did like Oikawa's gift. It was a bottle of cologne Iwaizumi had wanted and Oikawa had commented he'd like on Iwaizumi. But he has yet to open it—probably the sadist in him telling him to torture Oikawa just a bit more.

Oikawa sighs when he gets no response out of him. "All right… But," he continues, mirth lighting up his eyes, "you can't fake the worry I saw on your face earlier. Did you really believe I was leaving you for Yukio-chan or something?"

Urgh. Iwaizumi can almost feel the ulcer now. True, he's relieved that his imagination had blown things out of proportion, but now it's going to take all of his energy trying not to let Oikawa get too happy about the circumstances.

The setter eyes him, tea and Godzilla long forgotten. "Aw, don't be jealous, Iwa-chan~"

"I wasn't jealous!" Iwaizumi corrects gruffly. And he frowns. "But…" He sighs. "But this weird thing we have going on…"

Oikawa blinks. Then he blinks again, in disbelief. "You're joking, right?"

Iwaizumi glares at him.

Oikawa sighs happily, a laugh most certainly caught in his throat. He leans over so that his face is in Iwaizumi's. "Then, if you don't mind me starting to say it again, because I _really do_ mean it…I love you."

Well, hell. Iwaizumi wants to retort, to say something, to start his next sentence with "Shittykawa" or "Assikawa," but he can't, because Oikawa proceeds to show him just how much he loves him, and that his words aren't empty promises.

\- ^-^3

There are childhood friends. And then there are ambiguous relationships.

Iwaizumi Hajime now knows that things aren't as ambiguous between them as he once thought. And he has Oikawa Tooru to thank for filling in the blanks.

\- ^-^3

 **Someone stop me. It's now my head-canon that Iwa-chan and Kasamatsu-senpai are cousins and I just…** _ **I can't**_ **. D8 Also, does anybody else believe that Oikawa's probably an awful liar? XD But, man… So this was really silly, but I like that it has taken this long for Iwa-chan to believe that he and Oikawa are lovers, *lol*. This is also, I confess, a bit of *necessary* filler before the next story, which heralds the return of Kise on-screen, so for anyone who's read "Mutual Hate" and "Crossing Paths," the next fic's for you! And the one after that… *cackles evilly* No, really, I already know what I'm doing for the next two fics, which will have a larger KnB influence, so yeah.**

 **Thanks for reading, and please review! Check out my other fics (especially HQ! and KnB ones) if you liked this! I'm also pleased to announce I have a tumblr, le-amewzing (link on my FFN profile), where I cross-post my fics and post a lot of my art, so feel free to follow me there, too!**

 **-mew-tsubaki :]**


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